What's the best hub motor for an electric bike conversion?
September 12, 2010 6:02 PM   Subscribe

What's the best hub motor for converting a 28" single speed into an electric bike?

I have a chinese Flying Pigeon single speed bike (looks something like this for the curious: http://pic.dbw.cn/0/01/82/22/1822269_733284.jpg) and I'd like to add a pair of in-hub motors to turn it into an electric vehicle.

The problem is that all the kits for in-hub motors come with wheels that are too small (26" often.) I'm in China, so I could have someone custom-make me a wheel I guess, but I'm curious if anyone has a rec for a powerful and reliable in-hub motor. Money no object.

One more question I've been thinking about: if I have a motor on each wheel, how do I keep them at the same speed?
posted by maize to Technology (3 answers total)
Best answer: You don't need two hub motors on an electric bike. No one uses two because it would be extra weight, cost, and complexity for very little gain. Hub motors are very powerful and batteries only hold so much energy. Hub motors can provide 500W+ of power, while a typical cyclist outputs ~100W. You have plenty of power with one motor. On the other side of the equation, a typical battery might hold a few hundred Watt-hours. There is no point in adding a second motor, because you'll just deplete your batteries in a matter of minutes. Also, batteries have maximum safe power outputs that aren't usually very much. In short, the limiting factor is the battery, not the motor.

You do have a choice to make, which is if you prefer to front wheel or the rear to be powered. This is a trade-off. The front is easier to install, balances your bike better fore and aft (assuming you stick the battery on a rack, and give you all-wheel drive. The front can be squirrelly if everything is not quite true. The back is less likely to spin out on a gravel uphill (it has lots of weight on it), but it is more of a pain to install.

I imagine you can find a motor pre-built in a 28" wheel (those are quite common in China, aren't they?). If you can't, I wouldn't sweat having one handbuilt. Not only is the cost to build the wheel pretty insignificant once you buy the motor, controller, battery, cables, etc., but in my experience Chinese factory-built hub motor wheels are very poorly built and need a lot of work to get in reasonable shape, so you'll save time/money by having your wheel handbuilt anyways. Unless you want to spend a very large amount ($1000+) on a non-Chinese system, I recommend the Nine Continents motor. Ebikes.ca sells reasonable quality parts and has good information so if you can find the same stuff in China you should do well.
posted by ssg at 6:37 PM on September 12, 2010 [1 favorite]

Response by poster: Thanks very much for the (extremely complete) answer!
posted by maize at 7:57 PM on September 12, 2010

Just a guess ... but a 26 inch wheel could be installed into your bike without issues ... might be an easy solution
posted by jannw at 12:29 AM on September 13, 2010

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